Charge pump circuit with low reverse current and low peak current

ABSTRACT

A charge pump circuit includes a voltage input port, a voltage output port, a plurality of charge pump units cascaded between the voltage input port and the voltage output port, a clock signal source, and N clock delay elements. The clock signal source generates a main clock signal and the N clock delay elements generate clock signals received by the charge pump units by delaying the main clock signal. The main clock signal received by the first charge pump unit has a rising edge leading a rising edge of the last clock signal received by the last charge pump unit, and a falling edge lagging the rising edge of the last clock signal. Each of the charge pump units includes two sets of inverters with delay elements for generating two complementary clock signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority of U.S. provisionalapplication No. 62/341,105, filed on May 25, 2016, included herein byreference in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention is related to a charge pump circuit, especially to acharge pump with low reverse current and low peak current.

2. Description of the Prior Art

Due to requirements of low power for electronic devices, the powerspecification of integrated circuits (IC) is re-designed to work in alow voltage environment for reducing power consumption. For example, theIC power specification that used to be 5V before is now reduced to 3.3Vor even lower than 2V. Although lower voltages are supplied to reducepower consumption, greater voltages are still needed in some situations.For example, flash memory may require a greater voltage for programmingor erasing. The greater voltage is usually supplied by a charge pumpcircuit.

The charge pump circuits of prior art are usually controlled bycomplementary clock signals. The complementary clock signals are usuallygenerated by passing the main clock signals to two different signalpaths with different number of inverters. However, since the twogenerated clock signals are generated through different paths, the phasedifference between the two generated clock signals are usually not 180.Instead, one of the clock signals may lead the other clock signal. Theimperfect complementary clock signals will cause an unwanted reversecurrent of the charge pump circuit, increasing power consumption.Furthermore, to supply even higher voltages, the charge pump circuit hasseveral stages. In this case, a high peak current will occur if theclock signals are not controlled properly. Therefore, the control of theclock signals becomes complicated.

SUMMARY OF THE INVENTION

One embodiment of the present disclosure discloses a charge pump unit.The charge pump unit includes an input terminal, an output terminal, afirst N-type transistor, a second N-type transistor, a first P-typetransistor, a second P-type transistor, a first capacitor, a secondcapacitor, a clock input terminal, P first inverters, Q secondinverters, and R delay elements.

The first N-type transistor has a first terminal coupled to the inputterminal, a second terminal, and a control terminal. The second N-typetransistor has a first terminal coupled to the input terminal, a secondterminal coupled to the control terminal of the first N-type transistor,and a control terminal coupled to the second terminal of the firstN-type transistor. The first P-type transistor has a first terminalcoupled to the second terminal of the first N-type transistor, a secondterminal coupled to the output terminal, and a control terminal. Thesecond P-type transistor has a first terminal coupled to the secondterminal of the second N-type transistor and the control terminal of thefirst P-type transistor, a second terminal coupled to the outputterminal, and a control terminal coupled to the first terminal of thefirst P-type transistor.

The first capacitor has a first terminal coupled to the second terminalof the first N-type transistor, and a second terminal. The secondcapacitor has a first terminal coupled to the second terminal of thesecond N-type transistor, and a second terminal. The clock inputterminal receives a clock signal.

P first inverters are coupled in series between the clock input terminaland the second terminal of the first capacitor. R delay elements arecoupled in series with the Q second inverters between the clock inputterminal and the second terminal of the second capacitor. P and R arepositive integers, and Q is an integer smaller than P. The differencebetween P and Q is an odd number.

Another embodiment of the present disclosure discloses a charge pumpcircuit. The charge pump circuit includes a voltage input port, avoltage output port, a plurality of charge pump unit, a clock signalsource, and N clock delay elements.

The voltage input port receives an input voltage, and the voltage outputport outputs a pumped voltage. The plurality of charge pump units arecascaded between the voltage input port and the voltage output port.

The clock signal source generates a main clock signal. The N clock delayelements are coupled to the clock signal source and generate clocksignals received by the plurality of charge pump units by delaying themain clock signal. N is a positive integer.

The first charge pump unit of the plurality of charge pump receives themain clock signal. The main clock signal has a rising edge leading arising edge of a second clock signal received by the last charge pumpunit of the plurality of charge pump units coupled to the output port,and a falling edge lagging the rising edge of the second clock signal.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a charge pump unit according to one embodiment of thepresent disclosure.

FIG. 2 shows the waveforms of the clock signals used in the charge pumpunit of FIG. 1.

FIG. 3 shows an inverter according to one embodiment of the presentdisclosure.

FIG. 4 shows a delay element according to one embodiment of the presentdisclosure.

FIG. 5 shows a charge pump circuit according to one embodiment of thepresent disclosure.

FIG. 6 shows the waveforms of the clock signals used in the charge pumpcircuit of FIG. 5.

FIG. 7 shows a charge pump circuit according to another embodiment ofthe present disclosure.

DETAILED DESCRIPTION

FIG. 1 shows a charge pump unit 100 according to one embodiment of thepresent disclosure. The charge pump unit 100 includes an input terminalIN, an output terminal OUT, a first N-type transistor N1, a secondN-type transistor N2, a first P-type transistor P1, a second P-typetransistor P2, a first capacitor C1, a second capacitor C2, a clockinput terminal CLK, P first inverters 110, Q second inverters 120, and Rdelay elements 130. P is a positive integer, Q is a non-negative integersmaller than P, and R is a positive integer.

The first N-type transistor N1 has a first terminal, a second terminal,a control terminal, and a body terminal. The first terminal of the firstN-type transistor N1 is coupled to the input terminal IN. The secondN-type transistor N2 has a first terminal, a second terminal, a controlterminal, and a body terminal. The first terminal of the second N-typetransistor N2 is coupled to the input terminal IN, the second terminalof the second N-type transistor N2 is coupled to the control terminal ofthe first N-type transistor N1, and the control terminal of the secondN-type transistor N2 is coupled to the second terminal of the firstN-type transistor N1.

The first P-type transistor P1 has a first terminal, a second terminal,a control terminal, and a body terminal. The first terminal of the firstP-type transistor P1 is coupled to the second terminal of the firstN-type transistor N1, the second terminal of the first P-type transistorP1 is coupled to the output terminal OUT. The second P-type transistorP2 has a first terminal, a second terminal, a control terminal, and abody terminal. The first terminal of the second P-type transistor P2 iscoupled to the second terminal of the second N-type transistor N2 andthe control terminal of the first P-type transistor P1, the secondterminal of the second P-type transistor P2 is coupled to the outputterminal OUT, and the control terminal of the second P-type transistorP2 is coupled to the first terminal of the first P-type transistor P1.

The first capacitor C1 has a first terminal and a second terminal. Thefirst terminal of the first capacitor C1 is coupled to the secondterminal of the first N-type transistor N1. The second capacitor C2 hasa first terminal and a second terminal. The first terminal of the secondcapacitor C2 is coupled to the second terminal of the second N-typetransistor N2.

The clock input terminal CLK receives a clock signal SIG_(CLK). The Pfirst inverters 110 are coupled in series between the clock inputterminal CLK and the second terminal of the first capacitor C1. The Qsecond inverters 120 and the R delay elements 130 are coupled in seriesbetween the clock input terminal CLK and the second terminal of thesecond capacitor C2.

Also, a difference between P and Q is an odd number so that the clocksignal SIG_(CLKA) received by the first capacitor C1 and the clocksignal SIG_(CLKB) received by the second capacitor C2 would becomplementary to each other. For example, P can be 3 and Q can be 2. Toensure the phase difference between the clock signal SIG_(CLKA) and theclock signal SIG_(CLKB) remains 180 degrees, the R delay elements 130are coupled in series with the Q second inverters 120 between the clockinput terminal CLK and the second terminal of the second capacitor C2.The R delay elements 130 can be designed to provide a proper delay sothat the delay caused by the P first inverters 110 would besubstantially equal to the delay caused by the Q second inverters 120and the R delay elements 130. Therefore, clock signal SIG_(CLKA) and theclock signal SIG_(CLKB) can toggle at the same time, reducing thereverse current of the charge pump unit 100.

FIG. 2 shows the waveforms of the clock signal SIG_(CLKA) and the clocksignal SIG_(CLKB). In FIG. 2, during the period T1, the clock signalSIG_(CLKA) is at a first voltage VDD and the clock signal SIG_(CLKB) isat a second voltage VSS lower than the first voltage VDD. In someembodiments, the input terminal IN of the charge pump unit 100 may alsoreceive the first voltage VDD.

In the previous period before period T1, the first terminal of the firstcapacitor C1 may have been charged to the first voltage VDD through thefirst N-type transistor N1 while the second terminal of the firstcapacitor C1 is at the second voltage VSS. In period T1, since the clocksignal SIG_(CLKA) is raised to the first voltage VDD, the first terminalof the first capacitor C1 is raised to a third voltage 2VDD, which istwo times the first voltage VDD. Therefore, the second N-type transistorN2 is turned on, so the first terminal of the second capacitor C2 wouldbe charged to the first voltage VDD through the second N-type transistorN2 while the second terminal of the second capacitor C2 would follow theclock signal SIG_(CLKB) to be at the second voltage VSS.

In addition, the first P-type transistor P1 is turned on and the secondP-type transistor P2 is turned off. Therefore, the third voltage 2VDDwould be outputted to the output terminal OUT through the first P-typetransistor P1.

Similarly, in period T2, the clock signal SIG_(CLKA) is at the secondvoltage VSS and the clock signal SIG_(CLK2) is at the first voltage VDD.Since the first terminal of the second capacitor C2 has been charged tothe first voltage VDD through the second N-type transistor N2 in periodT1, the first terminal of the second capacitor C2 would be raised to thethird voltage 2VDD in period T2. Therefore, the first N-type transistorN1 is turned on, so the first terminal of the first capacitor C1 wouldbe charged to the first voltage VDD while the second terminal of thefirst capacitor C1 would follow the clock signal SIG_(CLKA) to be at thesecond voltage VSS.

In addition, the second P-type transistor P2 is turned on and the firstP-type transistor P1 is turned off. Therefore, the third voltage 2VDDwould be outputted to the output terminal OUT through the second P-typetransistor P2.

Consequently, the first P-type transistor P1 and the second P-typetransistor P2 can alternatively output the third voltage 2VDD, which istwo times the input voltage VDD. In prior art, if the clock signalSIG_(CLKA) and the clock signal SIG_(CLKB) do not toggle at the sametime, then the reverse current may occur. For example, if the clocksignal SIG_(CLKB) changes from the first voltage VDD to the secondvoltage VSS before the clock signal SIG_(CLKA) changes from the secondvoltage VSS to the first voltage VDD, then the clock signal SIG_(CLKA)and clock signal SIG_(CLKB) would be both at the second voltage VSS in ashort period. In this short period, both the first P-type transistor P1and the second P-type transistor P2 may be turned on, causing thereverse current to flow from the output terminal OUT back to the firstterminal of the first P-type transistor P1 and the first terminal of thesecond P-type transistor P2 through the first P-type transistor P1 andthe second P-type transistor P2.

However, since the delay caused by the P first inverters 110 would besubstantially equal to the delay caused by the Q second inverters 120and the R delay elements 130, the charge pump unit 100 can reduce thereverse current caused by the mismatched clock signals.

FIG. 3 shows an inverter INV according to one embodiment of the presentdisclosure. The P first inverters 110 and the Q second inverters 120each can have the same structure as the inverter INV. The inverter INVincludes an input terminal, an output terminal, a P-type transistor INVPand an N-type transistor INVN. The P-type transistor INVP has a firstterminal, a second terminal, and a control terminal. The first terminalof the P-type transistor INVP receives a first bias voltage, forexample, the first voltage VDD, the second terminal of the P-typetransistor INVP is coupled to the output terminal of the inverter INV,and the control terminal of the P-type transistor INVP is coupled to theinput terminal of the inverter INV. The N-type transistor INVN has afirst terminal, a second terminal, and a control terminal. The firstterminal of the N-type transistor INVN is coupled to the output terminalof the inverter INV, the second terminal of the N-type transistor INVNreceives the second bias voltage, for example, the second voltage VSS,and the control terminal of the N-type transistor INVN is coupled to theinput terminal of the inverter INV.

FIG. 4 shows a delay element DE according to one embodiment of thepresent disclosure. Each of the R delay elements 130 may have the samestructure as the delay element DE. The delay element DE includes aninput terminal, an output terminal, an N-type transistor DEN, and aP-type transistor DEP. The N-type transistor DEN has a first terminal, asecond terminal, and a control terminal. The first terminal of theN-type transistor DEN is coupled to the input terminal of the delayelement DE, the second terminal of the N-type transistor DEN is coupledto the output terminal of the delay element DE, and the control terminalof the N-type transistor DEN receives the first bias voltage, forexample, the first voltage VDD. The P-type transistor DEP has a firstterminal, a second terminal, and a control terminal. The first terminalof the P-type transistor DEP is coupled to the input terminal of thedelay element DE, the second terminal of the P-type transistor DEP iscoupled to the output terminal of the delay element DE, and the controlterminal of the P-type transistor DEP receives the second bias voltage,for example the second voltage VSS.

To provide the same delay as the inverter INV, the delay element DE maybe designed to have the channel width-to-length ratio of the N-typetransistor DEN substantially equal to the channel width-to-length ratioof the N-type transistor INVN of the inverter INV. Also, the channelwidth-to-length ratio of the P-type transistor INVP of the inverter INVcan be substantially equal to the channel width-to-length ratio of theP-type transistor DEP of the delay element DE.

In this case, if the P first inverters 110 and the Q second inverters120 are implemented by the inverter INV and the R delay elements 130 areimplemented by the delay element DE, then the sum of R and Q can beequal to P. Consequently, the delay caused by the P first inverters 110would be equal to the delay caused by the Q second inverters 120 and theR delay elements 130. For example, P can be 3, Q can be 2 and R canbe 1. Or, in another example, P can be 5, Q can be 2 and R can be 3.Moreover, the charge pump unit 100 may use first inverters 110 and delayelements 130 without using the second inverters 120. For example, P canbe 1, Q can be 0, and R can be 1. In this case, the first capacitor C1and the second capacitor C2 can still receive the complementary clocksignals with the same delay. Therefore, the reverse current can still beprevented.

Also, in some embodiments, the delay caused by the delay element 130 canbe different from the delay caused by the inverter 110 or 120, and thenumber of P, Q, and R can be adjusted according to the systemrequirement.

In FIG. 1, the charge pump unit 100 may further include a first initialpump transistor IT1 and a second initial pump transistor IT2. The firstinitial pump transistor IT1 has a first terminal, a second terminal, anda control terminal. The first terminal of the first initial pumptransistor IT1 is coupled to the input terminal IN of the charge pumpunit 100, the second terminal of the first initial pump transistor IT1is coupled to the second terminal of the first N-type transistor N1, andthe control terminal of the first initial pump transistor IT1 is coupledto the input terminal IN of the charge pump unit 100. The second initialpump transistor IT2 has a first terminal, a second terminal, and acontrol terminal. The first terminal of the second initial pumptransistor IT2 is coupled to the input terminal IN of the charge pumpunit 100, the second terminal of the second initial pump transistor IT2is coupled to the second terminal of the second N-type transistor N2,and the control terminal of the second initial pump transistor IT2 iscoupled to the input terminal IN of the charge pump unit 100.

The initial pump transistors IT1 and IT2 can be N-type transistors, andcan be used to charge the second terminals of the first N-typetransistor N1 and the second N-type transistor N2 to a voltage levelequal to VDD-Vthn, Vthn is the threshold voltage of N-type transistors,in the beginning of the charge pump process, ensuring the charge pumpunit 100 to become stable and output the pumped voltage faster.

Also, the charge pump unit 100 may further include a first pumpprecharge transistor TT1 and a second pump precharge transistor TT2. Thefirst pump precharge transistor TT1 has a first terminal, a secondterminal, and a control terminal. The first terminal of the first pumpprecharge transistor TT1 is coupled to the second terminal of the firstN-type transistor N1, the second terminal of the first pump prechargetransistor TT1 is coupled to the output terminal OUT of the charge pumpunit 100, and the control terminal of the first pump prechargetransistor TT1 is coupled to the output terminal OUT of the charge pumpunit 100. The second pump precharge transistor TT2 has a first terminal,a second terminal, and a control terminal. The first terminal of thesecond pump precharge transistor TT2 is coupled to the second terminalof the second N-type transistor N2, the second terminal of the secondpump precharge transistor TT2 is coupled to the output terminal OUT ofthe charge pump unit 100, and the control terminal of the second pumpprecharge transistor TT2 is coupled to the output terminal OUT of thecharge pump unit 100.

The pump precharge transistors TT1 and TT2 can be P-type transistors,and can be used to precharge the second terminals of the first P-typetransistor P1 and the second P-type transistor P2 when the charge pumpunit start pumping, reducing the output setting time of the charge pumpunit 100. For example, if the clock signal SIG_(CLKA) changes from thesecond voltage VSS to the first voltage VDD, the first terminal of thefirst capacitor C1 is raised to a third voltage 2VDD, the first pumpprecharge transistor TT1 can be used to charge the second terminals ofthe first P-type transistor P1 to a voltage level equal to 2VDD-Vthp,Vthp is the threshold voltage of P-type transistors, ensuring the chargepump unit 100 to become stable and output the pumped voltage faster.

In addition, to reduce body effect and to avoid the junction breakdownleakage current on the first N-type transistor N1, the charge pump unit100 may further include a first well switch WS1. The first well switchWS1 includes a third N-type transistor N3 and a fourth N-type transistorN4.

The third N-type transistor N3 has a first terminal, a second terminal,a control terminal, and a body terminal. The first terminal of the thirdN-type transistor N3 is coupled to the body terminal of the first N-typetransistor N1, the second terminal of the third N-type transistor N3 iscoupled to the second terminal of the first N-type transistor N1, thecontrol terminal of the third N-type transistor N3 is coupled to firstterminal of the first N-type transistor N1, and the body terminal of thethird N-type transistor N3 is coupled to the body terminal of the firstN-type transistor N1. The fourth N-type transistor N4 has a firstterminal, a second terminal, a control terminal, and a body terminal.The first terminal of the fourth N-type transistor N4 is coupled to thefirst terminal of the first N-type transistor N1, the second terminal ofthe fourth N-type transistor N4 is coupled to the body terminal of thefirst N-type transistor N1, the control terminal of the fourth N-typetransistor N4 is coupled to second terminal of the first N-typetransistor N1, and the body terminal of the fourth N-type transistor N4is coupled to the body terminal of the first N-type transistor N1.

With the well switch WS1, the voltage of the body terminal of the firstN-type transistor N1 can be controlled to be no greater than thevoltages of the first terminal and the second terminals of the firstN-type transistor N1. Therefore, the body effect and the leakage currentcaused on the body terminal of the first N-type transistor N1 can bereduced.

Similarly, in FIG. 1, the charge pump unit 100 may further include asecond well switch WS2, a third well switch WS3 and a fourth well switchWS4 for avoiding the leakage currents caused on the body terminals ofthe second N-type transistor N2, the first P-type transistor P1, and thesecond P-type transistor P2 respectively.

The second to fourth well switches WS2 to WS4 may have the similarstructure as the well switch WS1. That is, the second well switch WS2may include a fifth N-type transistor N5 and a sixth N-type transistorN6. The fifth N-type transistor N5 and the sixth N-type transistor N6may be coupled to the second N-type transistor N2 in the same manner asthe third N-type transistor N3 and the fourth N-type transistor N4coupling to the first N-type transistor N1.

Also, the third well switch WS3 may include a third P-type transistor P3and a fourth P-type transistor P4. The third P-type transistor P3 andthe fourth P-type transistor P4 may be coupled to the first P-typetransistor P1 in the same manner as the third N-type transistor N3 andthe fourth N-type transistor N4 coupling to the first N-type transistorN1. The fourth well switch WS4 may include a fifth P-type transistor P5and a sixth P-type transistor P6. The fifth P-type transistor P5 and thesixth P-type transistor P6 may be coupled to the second P-typetransistor P2 in the same manner as the third N-type transistor N3 andthe fourth N-type transistor N4 coupling to the first N-type transistorN1.

FIG. 5 shows a charge pump circuit 10 according to one embodiment of thepresent disclosure. The charge pump circuit 10 includes a voltage inputport VIN, a voltage output port VOUT, (N+1) charge pump units 1001 to100(N+1), a clock signal source 12, and N clock delay elements 141 to14N. N is a positive integer. The (N+1) charge pump units 1001 to100(N+1) are cascaded between the voltage input port VIN and the voltageoutput port VOUT. That is, a first charge pump unit 1001 of the (N+1)charge pump units 1001 to 100 (N+1) is coupled to the voltage input portVIN, and a last charge pump unit 100(N+1) of the (N+1) charge pump units1001 to 100(N+1) is coupled to the voltage output port VOUT.

In some embodiments, each of the charge pump units 1001 to 100(N+1) mayhave the same structure as the charge pump unit 100 as shown in FIG. 1.Therefore, with the voltage input port VIN receiving the first voltageVDD, the voltage output port VOUT can output a voltage that is (N+2)times the first voltage VDD, that is (N+2)VDD.

Also, with the structure shown in FIG. 1, the charge pump units 1001 to100(N+1) are able to produce two synchronized complementary clocksignals themselves according to the single clock signal received.

That is, when receiving the main clock signal SIG_(CLK1) generated bythe clock signal source 12, the charge pump units 1001 to 100(N+1) canproduce the two complementary clock signals accordingly. However, if thecomplementary clocks generated by the charge pump units 1001 to 100(N+1)are toggling simultaneously, then the capacitors of the charge pumpunits 1001 to 100 (N+1) would be charged at the same time, causing highpeak current each time when the two complementary clock signals toggle.Therefore, in FIG. 5, the N clock delay elements 141 to 14N are cascadedand coupled to the clock signal source 12 for generating the clocksignals required by the charge pump units 1002 to 100(N+1) by delayingthe main clock signal SIG_(CLK1). Also, each of the clock delay elements141 to 14N can produce a clock signal by delaying the received clocksignal with a predetermined period.

For example, the output terminal of the first clock delay element 141 iscoupled to the clock input terminal CLK of the second charge pump unit1002, and the output terminal of the second clock delay element 142 iscoupled to the clock input terminal CLK of the third charge pump unit1003. Also, the clock signal SIG_(CLK2) is outputted to the second clockdelay element 142 for generating the clock signal SIG_(CLK3) Therefore,the clock signal SIG_(CLK3) would be further delayed according to theclock signal SIG_(CLK2).

FIG. 6 shows the waveforms of the main clock signal SIG_(CLK1) generatedby the clock signal source 12 and the clock signals SIG_(CLK2) toSIG_(CLK(N+1)) generated by the clock delay elements 141 to 14N. In FIG.6, the main clock signal SIG_(CLK1) and the clock signals SIG_(CLK2) toSIG_(CL(N+1)) are toggled sequentially. For example, the main clocksignal SIG_(CLK1) has a rising edge RE1 leading the rising edge RE2 ofthe clock signal SIG_(CLK2), and the rising edge RE2 leads the risingedge RE3 of the clock signal SIG_(CLK3). Also, the rising edge RE1 ofthe clock signal SIG_(CLK1) leads the rising edge RE (i+1) of the clocksignal SIG_(CLK(i+1)), wherein i is an integer greater than 1 andsmaller than N+1. However, the main clock signal SIG_(CLK1) has afalling edge FE1 lagging the rising edge RE (N+1) of the second clocksignal SIG_(CLK(N+1)). Also, the falling edge FE1 leads the falling edgeFE2 of the clock signal SIG_(CLK2), and the falling edge FEi of theclock signal SIG_(CLK1) leads the falling edge FE (i+1) of the clocksignal SIG_(CLK (i+1)). That is, the clock signals SIG_(CLK2) toSIG_(CLK(N+1)) can be seen as a sequential of clock signals generated byshifting the main clock signal SIG_(CLK1).

In this case, the first charge pump unit 1001 receiving the main clocksignal SIG_(CLK1) would be charged first, the second charge pump unit1002 receiving the clock signal SIG_(CLK2) would be charged second, andso on. Consequently, the charge pump units 1001 to 100 (N+1) will not becharged at the same time, and the high peak current induced in the priorart can be avoided.

In FIG. 5, the charge pump units 1001 to 100(N+1) receive differentclock signals; however, in some embodiments, some of the charge pumpunits may receive the same clock signals for saving the area required bythe clock delay elements. FIG. 7 shows a charge pump circuit 20according to another embodiment of the present disclosure.

In FIG. 7, the structure of charge pump circuit 20 is similar to thestructure of the charge pump circuit 10. However, the charge pumpcircuit 20 includes (2N+2) charge pump units 1001 to 100 (2N+2). In thiscase, each pair of charge pump units would receive the same clocksignal. For example, the charge pump units 1001 and 1002 would receivethe main clock signal SIG_(CLK1), and the charge pump units 100 (2N+1)and 100 (2N+2) would receive the clock signal SIG_(CLK(N+1)). Therefore,as the number of charge pump units increases, the number of the clockdelay elements will increase in a slower rate, reducing the burden formeeting the area requirement of the charge pump circuit. However, themore charge pump units receive the same clock signal, the higher peakcurrent the charge pump circuit may produce. Therefore, the charge pumpcircuit can be designed to have different number of charge pump unitsreceiving the same clock signal according to the system requirement.

In summary, the charge pump units and the charge pump circuits providedby the embodiments of the present disclosure can use the delay elementsand inverters to generate complementary clock signals accurately,reducing the reverse current and simplifying the clock control of thecharge pump circuits. Furthermore, by delaying the clock signal of eachstage of charge pump unit in the charge pump circuit, the peak currentcan also be reduced significantly.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A charge pump unit comprising: an input terminal;an output terminal; a first N-type transistor having a first terminalcoupled to the input terminal, a second terminal, and a controlterminal; a second N-type transistor having a first terminal coupled tothe input terminal, a second terminal coupled to the control terminal ofthe first N-type transistor, and a control terminal coupled to thesecond terminal of the first N-type transistor; a first P-typetransistor having a first terminal coupled to the second terminal of thefirst N-type transistor, a second terminal coupled to the outputterminal, and a control terminal; a second P-type transistor having afirst terminal coupled to the second terminal of the second N-typetransistor and the control terminal of the first P-type transistor, asecond terminal coupled to the output terminal, and a control terminalcoupled to the first terminal of the first P-type transistor; a firstcapacitor having a first terminal coupled to the second terminal of thefirst N-type transistor, and a second terminal; a second capacitorhaving a first terminal coupled to the second terminal of the secondN-type transistor, and a second terminal; a clock input terminalconfigured to receive a clock signal; P first inverters coupled inseries between the clock input terminal and the second terminal of thefirst capacitor, wherein P is a positive integer; and R delay elementscoupled in series between the clock input terminal and the secondterminal of the second capacitor, wherein R is a positive integer. 2.The charge pump unit of claim 1, wherein a delay caused by the P firstinverters is substantially equal to a delay caused by the R delayelements.
 3. The charge pump unit of claim 1 further comprising Q secondinverters coupled in series with the R delay elements, wherein Q is apositive integer smaller than P and a difference between P and Q is anodd number.
 4. The charge pump unit of claim 3, wherein a delay causedby the P first inverters is substantially equal to a delay caused by theQ second inverters and the R delay elements.
 5. The charge pump unit ofclaim 3, wherein each of the R delay elements comprises: an inputterminal; an output terminal; an N-type transistor having a firstterminal coupled to the input terminal of the delay element, a secondterminal coupled to the output terminal of the delay element, and acontrol terminal configured to receive a first bias voltage; and aP-type transistor having a first terminal coupled to the input terminalof the delay element, a second terminal coupled to the output terminalof the delay element, and a control terminal configured to receive asecond bias voltage; wherein the first bias voltage is greater than thesecond bias voltage.
 6. The charge pump unit of claim 5, wherein each ofthe P first inverters and the Q second inverters comprises: an inputterminal; an output terminal; a P-type transistor having a firstterminal configured to receive the first bias voltage, a second terminalcoupled to the output terminal of the inverter, and a control terminalcoupled to the input terminal of the inverter; and an N-type transistorhaving a first terminal coupled to the output terminal of the inverter,a second terminal configured to receive the second bias voltage, and acontrol terminal coupled to the input terminal of the inverter; wherein:a channel width-to-length ratio of the N-type transistor of the inverteris substantially equal to a channel width-to-length ratio of the N-typetransistor of the delay element; and a channel width-to-length ratio ofthe P-type transistor of the inverter is substantially equal to achannel width-to-length ratio of the P-type transistor of the delayelement.
 7. The charge pump unit of claim 1, further comprising: a firstinitial pump transistor having a first terminal coupled to the inputterminal of the charge pump unit, a second terminal coupled to thesecond terminal of the first N-type transistor, and a control terminalcoupled to the input terminal of the charge pump unit; and a secondinitial pump transistor having a first terminal coupled to the inputterminal of the charge pump unit, a second terminal coupled to thesecond terminal of the second N-type transistor, and a control terminalcoupled to the input terminal of the charge pump unit.
 8. The chargepump unit of claim 1, further comprising: a first pump prechargetransistor having a first terminal coupled to the second terminal of thefirst N-type transistor, a second terminal coupled to the outputterminal of the charge pump unit, and a control terminal coupled to theoutput terminal of the charge pump unit; and a second pump prechargetransistor having a first terminal coupled to the second terminal of thesecond N-type transistor, a second terminal coupled to the outputterminal of the charge pump unit, and a control terminal coupled to theoutput terminal of the charge pump unit.
 9. The charge pump unit ofclaim 1, further comprising: a first well switch comprising: a thirdN-type transistor having a first terminal coupled to a body terminal ofthe first N-type transistor, a second terminal coupled to the secondterminal of the first N-type transistor, a control terminal coupled tofirst terminal of the first N-type transistor, and a body terminalcoupled to the body terminal of the first N-type transistor; and afourth N-type transistor having a first terminal coupled to the firstterminal of the first N-type transistor, a second terminal coupled tothe body terminal of the first N-type transistor, a control terminalcoupled to second terminal of the first N-type transistor, and a bodyterminal coupled to the body terminal of the first N-type transistor.10. The charge pump unit of claim 9, further comprising: a second wellswitch comprising: a fifth N-type transistor having a first terminalcoupled to a body terminal of the second N-type transistor, a secondterminal coupled to the second terminal of the second N-type transistor,a control terminal coupled to first terminal of the second N-typetransistor, and a body terminal coupled to the body terminal of thesecond N-type transistor; and a sixth N-type transistor having a firstterminal coupled to the first terminal of the second N-type transistor,a second terminal coupled to the body terminal of the second N-typetransistor, a control terminal coupled to second terminal of the secondN-type transistor, and a body terminal coupled to the body terminal ofthe second N-type transistor.
 11. The charge pump unit of claim 10,further comprising: a third well switch comprising: a third P-typetransistor having a first terminal coupled to a body terminal of thefirst P-type transistor, a second terminal coupled to the secondterminal of the first P-type transistor, a control terminal coupled tofirst terminal of the first P-type transistor, and a body terminalcoupled to the body terminal of the first P-type transistor; and afourth P-type transistor having a first terminal coupled to the firstterminal of the first P-type transistor, a second terminal coupled tothe body terminal of the first P-type transistor, a control terminalcoupled to second terminal of the first P-type transistor, and a bodyterminal coupled to the body terminal of the first P-type transistor.12. The charge pump unit of claim 11, further comprising: a fourth wellswitch comprising: a fifth P-type transistor having a first terminalcoupled to a body terminal of the second P-type transistor, a secondterminal coupled to the second terminal of the second P-type transistor,a control terminal coupled to first terminal of the second P-typetransistor, and a body terminal coupled to the body terminal of thesecond P-type transistor; and a sixth P-type transistor having a firstterminal coupled to the first terminal of the second P-type transistor,a second terminal coupled to the body terminal of the second P-typetransistor, a control terminal coupled to second terminal of the secondP-type transistor, and a body terminal coupled to the body terminal ofthe second P-type transistor.
 13. A charge pump circuit comprising: avoltage input port configured to receive an input voltage; a voltageoutput port configured to output a pumped voltage; a plurality of chargepump units cascaded between the voltage input port and the voltageoutput port; a clock signal source configured to generate a main clocksignal; and N clock delay elements coupled to the clock signal sourceand configured to generate at least one clock signal received by atleast one of the plurality of charge pump units by delaying the mainclock signal, wherein N is a positive integer; wherein: a first chargepump unit of the plurality of charge pump receives the main clocksignal; and the main clock signal has a rising edge leading a risingedge of a second clock signal received by a last charge pump unit of theplurality of charge pump units coupled to the output port, and a fallingedge lagging the rising edge of the second clock signal.
 14. The chargepump circuit of claim 13, wherein each of the plurality of charge pumpunits comprising: an input terminal; an output terminal; a first N-typetransistor having a first terminal coupled to the input terminal, asecond terminal, and a control terminal; a second N-type transistorhaving a first terminal coupled to the input terminal, a second terminalcoupled to the control terminal of the first N-type transistor, and acontrol terminal coupled to the second terminal of the first N-typetransistor; a first P-type transistor having a first terminal coupled tothe second terminal of the first N-type transistor, a second terminalcoupled to the output terminal, and a control terminal; a second P-typetransistor having a first terminal coupled to the second terminal of thesecond N-type transistor and the control terminal of the first P-typetransistor, a second terminal coupled to the output terminal, and acontrol terminal coupled to the first terminal of the first P-typetransistor; a first capacitor having a first terminal coupled to thesecond terminal of the first N-type transistor, and a second terminal; asecond capacitor having a first terminal coupled to the second terminalof the second N-type transistor, and a second terminal; a clock inputterminal configured to receive a clock signal; P first inverters coupledin series between the clock input terminal and the second terminal ofthe first capacitor, wherein P is a positive integer; and R delayelements coupled in series between the clock input terminal and thesecond terminal of the second capacitor, wherein R is a positiveinteger.
 15. The charge pump circuit of claim 14, wherein a delay causedby the P first inverters is substantially equal to a delay caused by theR delay elements.
 16. The charge pump circuit of claim 14, wherein eachof the plurality of charge pump units further comprises Q secondinverters coupled in series with the R delay elements, wherein Q is apositive integer smaller than P and a difference between P and Q is anodd number.
 17. The charge pump circuit of claim 16, wherein a delaycaused by the P first inverters is substantially equal to a delay causedby the Q second inverters and the R delay elements.
 18. The charge pumpcircuit of claim 17, wherein each of the P first inverters and the Qsecond inverters elements comprises: an input terminal; an outputterminal; a P-type transistor having a first terminal configured toreceive the first bias voltage, a second terminal coupled to the outputterminal of the inverter, and a control terminal coupled to the inputterminal of the inverter; and an N-type transistor having a firstterminal coupled to the output terminal of the inverter, a secondterminal configured to receive the second bias voltage, and a controlterminal coupled to the input terminal of the inverter; wherein: achannel width-to-length ratio of the N-type transistor of the inverteris substantially equal to a channel width-to-length ratio of the N-typetransistor of the delay element; a channel width-to-length ratio of theP-type transistor of the inverter is substantially equal to a channelwidth-to-length ratio of the P-type transistor of the delay element; anda sum of Q and R is equal to P.
 19. The charge pump circuit of claim 14,wherein each of the R delay elements comprises: an input terminal; anoutput terminal; an N-type transistor having a first terminal coupled tothe input terminal of the delay element, a second terminal coupled tothe output terminal of the delay element, and a control terminalconfigured to receive a first bias voltage; and a P-type transistorhaving a first terminal coupled to the input terminal of the delayelement, a second terminal coupled to the output terminal of the delayelement, and a control terminal configured to receive a second biasvoltage; wherein the first bias voltage is greater than the second biasvoltage.
 20. The charge pump circuit of claim 14, wherein each of theplurality of charge pump units further comprises: a first well switchcomprising: a third N-type transistor having a first terminal coupled toa body terminal of the first N-type transistor, a second terminalcoupled to the second terminal of the first N-type transistor, a controlterminal coupled to first terminal of the first N-type transistor, and abody terminal coupled to the body terminal of the first N-typetransistor; and a fourth N-type transistor having a first terminalcoupled to the first terminal of the first N-type transistor, a secondterminal coupled to the body terminal of the first N-type transistor, acontrol terminal coupled to second terminal of the first N-typetransistor, and a body terminal coupled to the body terminal of thefirst N-type transistor.
 21. The charge pump circuit of claim 14,wherein each of the plurality of charge pump units further comprises: asecond well switch comprising: a third P-type transistor having a firstterminal coupled to a body terminal of the first P-type transistor, asecond terminal coupled to the second terminal of the first P-typetransistor, a control terminal coupled to first terminal of the firstP-type transistor, and a body terminal coupled to the body terminal ofthe first P-type transistor; and a fourth P-type transistor having afirst terminal coupled to the first terminal of the first P-typetransistor, a second terminal coupled to the body terminal of the firstP-type transistor, a control terminal coupled to second terminal of thefirst P-type transistor, and a body terminal coupled to the bodyterminal of the first P-type transistor.
 22. The charge pump circuit ofclaim 13, wherein: the plurality of charge pump units comprise N+1charge pump units; and an output terminal of an i^(th) clock delayelement is coupled to a clock input terminal of an (i+1)^(th) chargepump unit; wherein N≧i≧1.